The present invention relates to an aluminum pipe for use in forming a plurality of bulged portions as aligned on the peripheral wall thereof at the same time by bulging, and a process for producing the pipe.
The term "aluminum" as used herein and in the appended claims includes pure aluminum and aluminum alloys.
For example, motor vehicle intake manifolds are considered to be useful which comprise, as shown in FIG. 1, a tubular plenum chamber 1 of aluminum extrudate having an open end and closed at the other end, the peripheral wall of the chamber having a plurality of holes 2 and integrally formed with tubular outward projections 3 around the respective holes 2, and a plurality of branch pipes 4 made of wrought aluminum and joined to the respective projections 3, each with its one end fitted in the projection.
It appears easy to produce the tubular plenum chamber 1 of the manifold by bulging the peripheral wall of an extruded aluminum pipe 5 by a single operation to form a plurality of tubular bulged portions 6 aligned in a row and each having a closed end (see FIG. 2), thereafter forming a hole in the closing end wall 7 of each tubular bulged portion 6, and subsequently outwardly bending the hole-defining portion of each end wall 7 and enlarging the outer end of the bent portion by bulging to thereby form the outward projections 3 for attaching the branch pipes to the chamber and form the holes 2.
For the production of the tubular plenum chamber 1, however, the bulged portions 6 to be formed on the peripheral wall of the extruded aluminum pipe 5 must be given a height which is at least 14% of the outside diameter of the pipe 5. As a result, it has been impossible for a single bulging operation to form such tubular bulged portions 6 as aligned on the peripheral wall of the extruded aluminum pipe 5 which is of the usual type because the great working ratio needed produces a fracture in the bulged portion 6.